Belts for monitoring body vital signs such as respiratory and cardiac activity are known. One such belt is described and shown in U.S. Pat. No. 3,268,845 and uses a variable resistance transducer. Another is shown in U.S. Pat. No. 4,494,553 and describes the use of multiple inductance coils. Others are shown in U.S. Pat. Nos. 4,121,575, 4,185,621, 3,782,368, 4,122,843 and 3,530,851.
The use of piezoelectric transducers for sensing respiratory function are well-known. See for example, U.S. Pat. Nos. 4,576,179, 3,782,368, 4,169,462, 4,185,621 and 4,443,730. These typically describe the use of piezo transducers that are sensitive to body breathing motions as well as impacts or forces incident from various directions.
In some devices piezoelectric transducers are used wherein a pair of piezo elements are connected so as to compensate either for pressure changes when temperature is to be sensed or for temperature when pressure is to be sensed. See for example, U.S. Pat. Nos. 3,940,974 and 3,187,300.
Various portable respiratory sensors that communicate with base units through rf communication links have been described, see U.S. Pat. No. 3,938,507. Systems have also been described for monitoring physiological parameters with devices that employ a microprocessor as in U.S. Pat. No. 4,356,825.